1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device using a plasma process and to a semiconductor device. In particular, it relates to a method of manufacturing a semiconductor device in which plasma damage after a step of forming a metal film, such as a wiring, is reduced and to a semiconductor device.
2. Description of the Related Art
In general, in manufacture of a semiconductor device on which various devices, such as a semiconductor element, a micromachine and a micro electro mechanical system (MEMS) are mounted, a plasma process, such as dry etching and ashing, is indispensable to meet requirements on the device, such as reduction of the two-dimensional size and formation of a three-dimensional structure.
When a plasma process is used in the process of manufacturing a semiconductor device, it is necessary to fully take into account the damage to an insulating film or the like caused by charges from the plasma accumulated on the substrate (referred to as plasma damage hereinafter).
In the device forming process, a plasma process may be used in a step of forming an interlayer insulating film before a metal wiring is formed or a step of removing a resist. However, the plasma damage in these steps is relatively small and can be eliminated by using a high-temperature annealing process. Thus, the plasma damage to the device is not significant.
On the other hand, for example, if reactive ion etching (RIE), which is a representative dry etching process that uses a plasma process, is used for forming a metal wiring, anisotropic processing according to the mask dimensions can be very advantageously achieved. However, because the metal film (the metal wiring, the electrode pad or the like) is exposed to the plasma during etching, charges in the plasma can be accumulated in the metal film to make the metal film electrically charged, and, as a result, a potential difference can occur between the metal film and the insulating film, causing degradation of the device characteristics or, in the worst case, an electric breakdown. Such plasma damage is a large problem concerning various devices, such as a semiconductor element and a micromachine. In addition, the metal film generally has a low melting point, so that the high-temperature annealing process cannot be used for the substrate after the metal film is formed, and therefore, it may be difficult to recover from the plasma damage to the insulating film or the like.
To solve the problem, for example, a non-patent literature (IEEE Transactions on Electron Devices, vol. 45, No. 4, 1998) discloses a technique of protecting a MOSFET, which is a representative semiconductor element, from plasma damage, according to which a source 1, a drain 2 and a gate 3 of the MOSFET and all pad electrodes 4 electrically connected to a substrate are connected to each other by a fuse wiring 5 (see FIG. 7). According to this technique, charges accumulated in the gate electrode during the plasma process are dissipated through the fuse wiring into the substrate from a substrate electrode electrically connected to a diffusion layer having the same conductive type as the semiconductor substrate or from a source electrode or a drain electrode electrically connected to the diffusion layer having the conductive type opposite to that of the semiconductor substrate, thereby reducing the plasma damage.